The morphological time sequence of chemical carcinogenesis in transitional epithelium lining urinary bladder has been characterized in rat models. Due to the microscopically thin nature of the tissue in vivo it has been difficult to conduct physiological, biochemical, and morphological studies that precisely describe and compare the normal mechanisms of growth and differentiation to those of the carcinogenic process. An epithelial growth system which allows the growth, stratification, differentiation, and maintenance of homogeneous, adult Fischer-344 rat transitional epithelium in vitro has been developed. Using this system it is proposed: 1. to further define the requirements and factors governing growth, stratification, differentiation, and maintenance of normal tissue; 2. to determine the biological mechanism of carcinogenesis; and 3. to determine whether human transitional epithelium will grow and differentiate in the epithelial growth system. The normal tissue studies will include: continued development of a defined media; evaluation of porous growth surfaces; examination of the apparent differentiation-inducing effects of urine; determination of permeability characteristics; and resolution of the role of hormone-stimulated cyclic AMP metabolism in normal tissue. The carcinogenesis studies will include: determination of efficacious carcinogens; definition of morphological staging of in vitro carcinogenesis; assessment of the role of promoters; and analysis of a variety of events important in a two-stage mechanism of carcinogenesis (e.g., dose effects, sequence, reversibility-irreversibility; cell division, etc.). Tumorigenicity of in vitro transformed cell lines will be determined by back-transplantation. The human cell culture studies will utilize remnants of routine bladder punch-biopsies and will be carried out exactly as described for the rat epithelial growth system. These studies are being carried out to lay the foundation for determination of the molecular mechanism of chemical carcinogenesis of transitional epithelium.